Are there any guides out yet?
The in game quests guide you pretty well follow the childhood friend quests for a short but loving story and do the other characters instead for the true ending. The only thing they don't really mention is that most girls quests have compensated dating rankings required before their quest will start so keep sending girls out when they have 0 stress so they gain development points (ranking is basically 100% determined by how many girls you have above level 1). Keep getting pregnant as often as possible and following the quests until you can unlock corrupting other girls, then focus on making sure they're all popping out as many kids as possible to allow for more corruptions. The only girls that aren't extremely straight forward are
The convenience store girl:
1. See her lose the tickets
2. Find the first ticket outside and turn it into her (you need to buy the bus pass to make the bus molester quit)
3. find the other 4 tickets as follows and then turn those in
a. In the park
b. In the rape alleyway west of your apartment(go during the day)
c. In your father's company (go during the day)
d. In the 3rd floor classroom (can only enter after school, you need to do something there that day, you can't enter if you didn't go or you've already left for the day)
The delinquent:
This is the one most people have trouble with. She appears on the roof during the day at school. There might be a rank requirement but she should unlock fairly early. After that you get a real quest and can just follow it.
The exchange student:
You'll have a proper quest for this one but she's in the shopping district, then the park, then near the old apartment building.
You can find this in game but the true ending of the game requires completely following the fallen story line until you produce both porn vids, corrupting all non-hired girls into being nympho's, and reaching rank 1. This means you need to be sending out girls as often as you can when they have 0 stress. Recruiting as many as possible before you unlock sex dating is key here. When you unlock that there will only be 2 non-sex options daily, so getting as many girls as high up as possible before then is massive. Additionally you will want to have any girls give birth before you send out assignments for the day. Every time you get 3 samples you need to convert a girl asap and work on getting her pregnant (check which ones are not stressed before you decide who to convert.
If you want to do it all in one run you will need to be serious from the start, but if you do some of the other routes first you can use those runs to focus on earning stars so you can buy the permanent buff items with the clear bonus.
Also Kagura is ass and managed to put a memory leak so save often (including any time you want to check your stats page to check your ranking) or just use Dazed's translation.